Justification

If the same Django user is logged in twice on different computers simultaneously, they see each others' messages

User messages may get wiped even if they're not actually displayed to the user

High-load sites want to avoid the unneeded database or cache usage

Reasons why a standard needs to be endorsed by Django and a 3rd party app will not suffice:

The built-in implementation is broken for a large set of use cases (above); the fact that Django actively encourages this method of messaging is a bad thing

Reusable apps don't know what 3rd party system to use and hence cannot rely on providing session feedback

Integrating with the Existing API

It is not possible nor desirable to integrate with the existing API because it is tied directly to a related manager on the user model and cannot be extended to support the additional functionality in this proposal (without some ugly hacks). There are several possible solutions to this conflict (we don't really need or want two messaging APIs in the core); feel free to add more:

In the documentation, cast the user messaging API in a vary narrow use; e.g., for administrator messages to specific users

Phase out user messages entirely

Existing 3rd Party Apps

There are a number of good, pre-existing applications out there that support more robust functionality, so there is no need to re-implement a solution from scratch for inclusion in Django. The existing solutions can be combined or modified to meet Django's needs. This section is meant to evaluate some of the different session/cookie message/notification engines out there for potential inclusion in Django as a contrib app. It is a work in progress so please contribute (your notification engine here) or other changes as you see fit.

Criteria

Technical criteria necessary for inclusion in the core:

Support message passing for anonymous users

Use the session only as a fallback: Avoid database/cache queries if possible, but support larger messages that don't fit in a cookie (> 4kb) when needed

Don't lose messages if they're not displayed to the user (lazy message loading)

django-notify

django-notify is the current front-runner in terms of technical features so a sampling of the potential API is included below. Feel free to include the API(s) of other solutions as well for comparison. It is understood that, should django-notify be chosen, this may (and probably will) change prior to inclusion in the core.

request.notifications.add('Hello world.')
# You can optionally provide a string containing tags (which is usually represented as HTML classes for the message).
request.notifications.add('Your rating is over 9000!', 'error')